1. Field of the Invention
This invention pertains generally to delivery of medicinal aerosols for inhalation therapy, and more particularly to an apparatus for delivering medicinal aerosols to a patient on demand during inhalation.
2. Description of the Background Art
It is known that the thin membrane of the lungs can be easily penetrated by medicinal aerosols and provides a convenient and generally safe vehicle for obtaining rapid absorption of medication by the body. Medication or drugs are generally delivered to the lung membrane in the form of a fine mist or aerosol which is breathed into the lungs through the nose or mouth of the patient. Quite typically, a nebulizer is used to convert a liquid into a fine aerosol, and the aerosol is introduced into the lungs by means of a mouthpiece which delivers the aerosol through the mouth only, or by means of a face mask which delivers the aerosol through both the mouth and nose of the patient. However, conventional delivery systems provide a continuous flow of aerosol and, as a result, a portion of the aerosol is wasted during exhalation of the patient. Furthermore, the wasted medicinal aerosol is exhausted into the ambient air, thereby creating environmental risks as well as risking the health and safety of health care workers who breath the surrounding air. Also, bacteria and other materials present in the patient's exhalation gas are permitted to escape. Heretofore, inhalation booths or tents with laminar flow hoods and filtration systems have been used to guard against those risks. However, such devices are expensive and bulky, and still do not protect the health care workers who must enter the tent or hooded area.
Various such inhalation devices have been previously developed. For example, U.S. Pat. No. 4,823,784 issued to Bordoni et al. on Apr. 25, 1989, discloses an aerosol inhalation apparatus which runs continuously and does not provide for synchronization of delivery with the patient's breathing cycle. Further, the device requires use of a filter to remove or reduce the amount of unused aerosolized medicament discharged into the ambient air. The filter provides a flow restriction thereby impeding exhalation and increasing discomfort, and is subject to occlusion from fluids in the exhalation gas. U.S. Pat. No. 4,106,503 issued to Rosenthal et al. on Aug. 15, 1978, discloses a metering system for stimulating bronchial spasm which delivers a metered dose of nebulized antigen during inhalation but must be manually activated with a switch. U.S. Pat. No. 4,677,975 issued to Edgar et al. on Jul. 7, 1987, discloses a method and apparatus for dispensing inhalable material which tells the patient when to inhale or exhale based on timed intervals and delivers the inhalable material during inhalation. The device does not administer medicament in synchronization with a normal breathing cycle. U.S. Pat. No. 5,080,093 issued to Raabe et al. on Jan. 14, 1992 and U.S. Pat. No. 4,832,012 issued to Raabe et al. on May 23, 1989, disclose intermittent signal actuated nebulizers in which electrical signals from a respirator device are sensed and used to trigger delivery of medicinal aerosol.
As can be seen, therefore, a need exists for an aerosol delivery apparatus which initiates delivery of medicine only at the beginning of the inhalation cycle, and which prevents delivery of medicine during the exhalation cycle. The present invention satisfies that and other needs, and overcomes the deficiencies in devices heretofore developed.